This invention relates to a relief image scanner for reading or capturing a relief image from the surface of an information-carrying medium such as a plastic card or metal plate.
Plastic cards such as credit cards, bank cards, and hospital patient cards are often embossed with raised letters and numbers giving a name, identification number, account number, or other information. Alternatively, such information may be stamped into the card, the letters and numbers being formed as depressions in the surface of the card. It is often desirable to transfer the information to an electronic data-processing system, for which purpose the surface of the card must be scanned by a device capable of detecting embossed or stamped patterns. (Such patterns will be referred to generally as relief patterns below.) At the same time it may be desirable to capture information printed or otherwise provided on flat portions of the card, such as the card owner's signature and photograph. (Such information will generally be referred to as printed information below.)
Prior-art apparatus for capturing images of relief patterns comprises a television camera and four light sources. The four light sources, which are disposed around the four sides of the card, illuminate the card from four directions in succession. When each light source is turned on, the relief casts shadows which are detected by the television camera and stored in a memory. The four shadow images are then combined by OR logic, yielding a total image of the relief.
This apparatus is unsatisfactory due to its large size, since it requires four separate light sources. The television camera is also large and expensive.
A further problem is that since the angles of illumination vary at different positions on the card, the shadows are of different lengths, which distorts the image.
Another type of image distortion that often occurs is that the captured image shows only the outlines of the relief. If the relief comprises depressions, outline images are formed when the depressions are so wide that they are not entirely filled by the shadows. If the relief comprises raised characters, then outline images are always formed, and there is a tendency for the outlines of adjacent characters to run together. Such outline images look unnatural to the eye, and are difficult for computer-based character recognition systems to identify accurately.
Still another problem occurs if the card also contains printed information or a printed background pattern, which may be mistaken by the television camera for part of the relief pattern.
Yet another problem is that the prior-art apparatus is unsuitable for capturing images of printed information, which must accordingly be acquired by a separate scanner.